What Is The By Product Of Cellular Respiration?


Cellular respiration is an aerobic process by which living cells breaks down glucose molecules and releases energy.

Cellular respiration occurs in the cells of all living things, both autotrophs and heterotrophs.

Processes And By Product Of Cellular Respiration

Cellular respiration is the process by which organisms combine oxygen with food molecules, directing the chemical energy contained in these substances to life and releasing it as by products, carbon dioxide, and water. Organisms that do not depend on oxygen decompose food in a process called fermentation.

Cellular respiration contains many chemical reactions, but they are all combined with this chemical equation:


Release of energy during cellular respiration

The equation above shows that glucose (C6H12O6C6H12O6) and oxygen (O2O2) react to form carbon dioxide (CO2CO2) and water H2OH2O, releasing energy in the process. Because oxygen is required for cellular respiration, it is an aerobic process.

The reactions of cellular respiration can be grouped into three stages: glycolysis, the Krebs cycle, and electron transport.


Glycolysis (also known as the glycolytic or Embden-Meyerhoff-Parnassus pathway) is a sequence of 10 chemical reactions occurring in most cells that breaks down a molecule of glucose into two molecules of pyruvate (pyruvic acid).

The energy released by the breakdown of glucose molecules and other organic fuel molecules from carbohydrates, fats and proteins during glycolysis is captured and stored in ATP.

In addition, the nicotinamide adenine dinucleotide (NAD+) compound is converted into NADH during this process.

The pyruvate molecules formed during glycolysis then enter the mitochondria, where each is converted into a compound known as acetylcoenzyme A, which then enters the TCA cycle.

(Some sources consider the conversion of pyruvate to acetyl coenzyme A as a separate step, called pyruvate oxidation or transient reaction, in the process of cellular respiration.)

Kreb’s Cycle

The Kreb’s Cycle plays a central role in the breakdown, or catabolism, of organic fuel molecules.

The cycle consists of eight steps, catalyzed by eight different enzymes, which produce energy in several different steps.

However, most of the energy produced in the TCA cycle is captured by NAD+ and adenine flavin dinucleotide (FAD) compounds and subsequently converted into ATP.

The products of one turnover of the TCA cycle consist of three NAD+ molecules, which are reduced (through the process of adding hydrogen, H+) to the same number of NADH molecules, and one FAD molecule, which is similarly reduced to one FADH2 molecule.

These molecules continue to feed the third stage of cellular respiration, while carbon dioxide, which is also produced by the TCA cycle, is released as a waste product.

Electron Transport Chain

In this step, high-energy electrons are released from NADH and FADH2, which move along electron-transport chains on the inner mitochondrial membrane.

The electron-transport chain is a series of molecules that transport electrons from molecule to molecule by chemical reactions.

Part of the energy derived from the electrons is used to transfer hydrogen ions (H+) across the inner membrane, from the matrix to the intermembrane space.

This ion transfer creates an electrochemical gradient leading to ATP synthesis.


During cellular respiration, carbon dioxide and water are mainly the by-products of this aerobic process.



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